memcached udp datagram size and noreply option support

Erik Ljungstrom erik at
Sun May 4 00:50:26 UTC 2008


The MTU is normally set on your network interfaces (and possibly  
subsequent network devices depending on your setup) rather than in  
individual applications. How you do it obviously depends on what OS  
you're running. On Linux, *BSD and Solaris you'd typically do:  
ifconfig [interface] mtu [value] where value is the maximum number of  
bytes which can be sent in one go through that interface. So the  
default 1500 means that packets will be fragmented if they exceed 1500  

I do however recommend that you do a bit of research to avoid negative  
surprises such as upstream devices refusing to deal with too large  
units etc!


On 4 May 2008, at 00:59, Dongni Chen wrote:

> Hi,
> I understand the network impact. So if we already considered the  
> network issue, and still want to increase the MTU size, is there an  
> option to turn on bigger MTU size?
> Thanks!
> Dogni
> ----- Original Message ----
> From: Tomash Brechko <tomash.brechko at>
> To: memcached at
> Sent: Saturday, May 3, 2008 9:11:26 AM
> Subject: Re: memcached udp datagram size and noreply option support
> On Sat, May 03, 2008 at 08:25:35 -0700, Dongni Chen wrote:
> > I am currently running memcached 1.2.4 and want to use "Set" with
> > "noreply" option. But seems it doesn't support. Shall I move to
> > 1.2.5 to get this feature?
> Yes, noreply is supported starting with memcached 1.2.5.
> > I am also use udp mode, and found out even for a data size that is
> > about 1.9k, I am getting 2 datagrams. I used memcached -vv, and it
> > says when in udp mode, the sendbuf is 268435456.
> Maximum Transfer Unit (MTU) is still limited to some smaller value,
> likely 1500 bytes.  Though it's possible to increase it up to 64KB,
> doing so will likely have strong negative effect on your network.  In
> other words, better to leave it as is, and deal with multiple packets,
> or switch back to TCP.  If you are trying to save on TCP connection
> establishing, it would be better to think about ways to cache and
> reuse the connection.
> -- 
>   Tomash Brechko
> Be a better friend, newshound, and know-it-all with Yahoo! Mobile.  
> Try it now.

More information about the memcached mailing list